Effects of thawing-induced softening on fracture behaviors of frozen rock

Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.

A dynamic soil freezing characteristic curve model for frozen soil

The soil freezing characteristic curve(SFCC)plays a fundamental role in comprehending thermohydraulic behavior and numerical simulation of frozen soil.This study proposes a dynamic model to uniformly express SFCCs amidst varying total water contents throughout the freezing-thawing process.Firstly,a general model is proposed,wherein the unfrozen water content at arbitrary temperature is determined as the lesser of the current total water content and the reference value derived from saturated SFCC.The dynamic performance of this model is verified through test data.Subsequently,in accordance with electric double layer(EDL)theory,the theoretical residual and minimum temperatures in SFCC are calculated to be-14.5℃to-20℃for clay particles and-260℃,respectively.To ensure that the SFCC curve ends at minimum temperature,a correction function is introduced into the general model.Furthermore,a simplified dynamic model is proposed and investigated,necessitating only three parameters inherited from the general model.Additionally,both general and simplified models are evaluated based on a test database and proven to fit the test data exactly across the entire temperature range.Typical recommended parameter values for various types of soils are summarized.Overall,this study provides not only a theoretical basis for most empirical equations but also proposes a new and more general equation to describe the SFCC.

Experimental and numerical interpretation on composite foundation consisting of soil-cement column within warm and ice-rich frozen soil

Affected by climate warming and anthropogenic disturbances, the thermo-mechanical stability of warm and ice-rich frozen ground along the Qinghai-Tibet engineering corridor(QTEC) is continuously decreased, which may delay the construction of major projects in the future. In this study, based on chemical stabilization of warm and icerich frozen ground, the soil-cement column(SCC) for ground improvement was recommended to reinforce the foundations in warm and ice-rich permafrost regions. To explore the validity of countermeasures mentioned above, both the original foundation and the composite foundation consisting of SCC with soil temperature of -1.0℃ were prepared in the laboratory, and then the plate loading tests were carried out. The laboratory investigations indicated that the bearing capacity of composite foundation consisting of SCC was higher than that of original foundation, and the total deformation of original foundation was greater than that of composite foundation, meaning that overall stability of foundation with warm and ice-rich frozen soil can be improved by SCC installation. Meanwhile, a numerical model considering the interface interaction between frozen soil and SCC was established for interpretating the bearing mechanism of composite foundation. The numerical investigations revealed that the SCC within composite foundation was responsible for the more applied load, and the applied load can be delivered to deeper zone in depth due to the SCC installation, which was favorable for improving the bearing characteristic of composite foundation. The investigations provide the valuable guideline for the choice of engineering supporting techniques to major projects within the QTEC.

Mechanical behaviors of warm and ice-rich frozen soil stabilized with sulphoaluminate cement

The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.

Experiment and constitutive modelling of creep deformation in the frozen silt-concrete interface

To ensure the long-term safety and stability of bridge pile foundations in permafrost regions,it is necessary to investigate the rheological effects on the pile tip and pile side bearing capacities.The creep characteristics of the pile-frozen soil interface are critical for determining the long-term stability of permafrost pile foundations.This study utilized a self-developed large stress-controlled shear apparatus to investigate the shear creep characteristics of the frozen silt-concrete interface,and examined the influence of freezing temperatures(−1,−2,and−5°C),contact surface roughness(0,0.60,0.75,and 1.15 mm),normal stress(50,100,and 150 kPa),and shear stress on the creep characteristics of the contact surface.By incorporating the contact surface’s creep behavior and development trends,we established a creep constitutive model for the frozen silt-concrete interface based on the Nishihara model,introducing nonlinear elements and a damage factor.The results revealed significant creep effects on the frozen silt-concrete interface under constant load,with creep displacement at approximately 2-15 times the instantaneous displacement and a failure creep displacement ranging from 6 to 8 mm.Under different experimental conditions,the creep characteristics of the frozen silt-concrete interface varied.A larger roughness,lower freezing temperatures,and higher normal stresses resulted in a longer sample attenuation creep time,a lower steady-state creep rate,higher long-term creep strength,and stronger creep stability.Building upon the Nishihara model,we considered the influence of shear stress and time on the viscoelastic viscosity coefficient and introduced a damage factor to the viscoplasticity.The improved model effectively described the entire creep process of the frozen silt-concrete interface.The results provide theoretical support for the interaction between pile and soil in permafrost regions.

Analysis and Utilization of Straw-preserved Frozen Semen from Native and Imported Pig Breeds in Guizhou Province

[Objectives]Straw-preserved frozen semen from native and imported pig breeds and its conception performance were studied to provide a scientific basis for further optimizing pig breeding strategy.[Methods]This study was conducted to systematically evaluate straw-preserved frozen semen produced by the Guizhou Testing Center for Livestock and Poultry Germplasm from 2018 to 2023.We analyzed 206 samples from native Guizhou pig breeds,including Kele,Zongdi Hua,and Nuogu pigs,as well as 363 samples from imported and bred pig breeds,such as Duroc,Large Yorkshire,Landrace,Topigs,and French Yorkshire,among others.Additionally,we assessed the conception performance of more than 300 heads across 10 batches,comprising both native and imported and bred pig breeds,following deep insemination.[Results]Significant differences were identified in sperm motility and abnormal sperm percentage(ABSP)among native breeds(P<0.05),as well as in number of progressively motile sperm(NPMS)and ABSP among imported and bred breeds(P<0.05).The average semen dose for both native and imported/bred pigs was 0.47 ml,with a standard deviation of 0.01 ml.Sperm motility ranged from 41.5%to 58%in native breeds and 50.4%to 61.7%in imported and bred breeds.The NPMS ranged from 144 to 177 million in native breeds and 149 to 177 million in imported and bred breeds.ABSPs remained within acceptable limits,ranging from 6.6%to 16.8%for native breeds and 6.1%to 18.1%for imported and bred breeds.The imported and bred pigs outperformed the native breeds in terms of sperm motility(50.42%to 69.58%vs.41.63%to 48.37%),farrowing rate(71.13%to 86.70%vs.57.15%to 74.35%),and litter size(7.74 to 10.30 vs.6.39 to 7.45).[Conclusions]These findings suggest that long-term selective breeding and domestication of native Guizhou pigs are necessary to enhance their reproductive performance.

REVIEW OF ACUPUNCTURE FOR FROZEN SHOULDER

Objective To assess the efficacy and possible adverse effects of acupuncture on frozen shoulder. Methods Based on the key words, i.e. acupuncture, electroacupuncture, acupuncture-moxibustion, frozen shoulder, adhesive capsulitis, shoulder disorders etc., the Chinese databases were retrieved, including Oochrane Musculoskeleta Group, Oochrane Controlled Trials Register, Oochrane Complementary Medicine Field, and the central database of the Oochrane Library as well as MEDLINE, EMBASE and Chinese Biomedical CD （OBM-disc）. 20 Chinese medical journals and relevant academic conference proceedings have been searched manually. The reference lists of identified documents were checked as the supplementary retrieval. Results 6 randomized controlled trials on frozen shoulder with acupuncture and electroacupuncture were included, indicating quite advanced study quality. There were 34 to 257 participants in the trials, 668 in total. The total OR of CMS/OSA was OR 3.49 （95 % CI - 2.64 to 9.63）, the total OR of VAS was OR - 1.24 （95% CI -3.50 to 1.01）, the total OR of ROM was OR 35.70 （95% CI 22.91 to 48.49）; the total OR of MELLE was OR 4.30 （95% OI 2.32 to 7.98）. Conclusion It is shown in the present limited inclusive trials on frozen shoulder that acupuncture is the safe therapy and effective on improving the global function, relieving pain, and improving the range of motion of shoulder. All the therapeutic effects of acupuncture are superior to those in control group. However, much more high quality trials are required to provide much stronger evidence. Additionally, much more evidences on validity of frozen shoulder with other assessing indexes involved are required in the treatment with acupuncture.

An experimental study on the relationship between acoustic parameters and mechanical properties of frozen silty clay

To study the influence of temperature and water content on ultrasonic wave velocity and to establish the relationship between ultrasonic wave velocity and frozen silty clay strength, ultrasonic tests were conducted to frozen silty clay by using RSM-SY5（T） nonmetal supersonic test meter, and the tensile strength and compressive strength of silty clay were measured under various negative temperatures. Test and analysis results indicate that, ultrasonic wave velocity rapidly changes in the temperature range of-1 ℃ to -5 ℃. Ultrasonic wave velocity increased with an increase of water content until the water content reached the critical water content, while decreased with an increase of water content after the water content exceeded the critical water content. This study showed that there was strong positive correlation between the ul- trasonic wave velocity and the frozen soil strength. As ultrasonic wave velocity increased, either tensile strength or com- pressive strength increased. Based on the experimental data, the relationship between ultrasonic wave velocity and frozen silty clay strength was obtained through regression analysis. It was found that the ultrasonic test technique can be used to test frozen soils and lay the foundation for the determination of frozen soil strength.

Hysteresis in the ultrasonic parameters of saturated sandstone during freezing and thawing and correlations with unfrozen water content

Determining the mechanical properties of frozen rock is highly important in cold-area engineering.These properties are essentially correlated with the content of liquid water remaining in frozen rock.Therefore,accurate determination of unfrozen water content could allow rapid evaluation of mechanical properties of frozen rock.This paper investigates the hysteresis characteristics of ultrasonic waves applied to sandstone(in terms of the parameters of P-wave velocity,amplitude,dominant frequency and quality factor Q)and their relationships with unfrozen water content during the freeze-thaw process.Their correlations are analysed in terms of their potential for use as indicators of freezing state and unfrozen water content.The results show that:(1)During a freeze-thaw cycle,the ultrasonic parameters and unfrozen water content of sandstone have significant hysteresis with changes in temperature.(2)There are three clear stages of change during freezing:supercooled stage(0℃to-2℃),rapid freezing stage(-2℃to-3℃),and stable freezing stage(-3℃to-20℃).The changes in unfrozen water content and ultrasonic parameters with freezing temperature are inverse.(3)During a single freeze-thaw cycle,the ultrasonic parameters of sandstone are significantly correlated with its unfrozen water content,and this correlation is affected by the pore structure.For sandstones with mesopores greater than 50%,there are inflection points in the curves of ultrasonic parameters vs.unfrozen water content at-3℃during freezing and at-1℃during thawing.It was found that thermal deformation of the mineral-grain skeleton and variations in the phase composition of pore water change the propagation path of ultrasonic waves.The inflection point in the curve of dominant frequency vs.temperature clearly marks the end of the rapid freezing stage of pore water,in which more than 70%of the pore water freezes.Consequently,the dominant frequency can be used as an index to conveniently estimate the unfrozen water content of frozen rock and,hence,its mechanical properties.

Effect of weak magnetic field on the water-holding properties,texture,and volatile compounds of pork and beef during frozen storage

The weak magnetic field has recently attracted much attention for improving the quality of frozen food due to its mild effectiveness and near-complete transmission through the food matrix.This study aimed to explore the effect of the magnetic field with 1 mT and 50 Hz on the freezing process and storage quality of pork and beef.The results showed that the freezing point of beef stored under the magnetic field was-1.7℃,which was 0.5℃ lower than that of conventional frozen(CF)groups,and the phase transition times of pork and beef were reduced by 55.56%and 50.00%,respectively.The magnetic field maintained higher water-holding capacity and decreased drip loss and cooking loss for both types of meat.Coherently,the evaporation and redistribution of water was inhibited by MF,as indicated by the magnetic resonance imaging results.The magnetic field also effectively moderated the hardening in texture,odor deterioration and color change of frozen pork and beef.Less accumulation of free amino acids suggested the degradation of protein was suppressed under magnetic field.The present study would provide a scientific reference for the application of weak magnetic field in meat preservation.

Coupling numerical simulation with remotely sensed information for the study of frozen soil dynamics

The acquisition of spatial-temporal information of frozen soil is fundamental for the study of frozen soil dynamics and its feedback to climate change in cold regions.With advancement of remote sensing and better understanding of frozen soil dynamics,discrimination of freeze and thaw status of surface soil based on passive microwave remote sensing and numerical simulation of frozen soil processes under water and heat transfer principles provides valuable means for regional and global frozen soil dynamic monitoring and systematic spatial-temporal responses to global change.However,as an important data source of frozen soil processes,remotely sensed information has not yet been fully utilized in the numerical simulation of frozen soil processes.Although great progress has been made in remote sensing and frozen soil physics,yet few frozen soil research has been done on the application of remotely sensed information in association with the numerical model for frozen soil process studies.In the present study,a distributed numerical model for frozen soil dynamic studies based on coupled water-heat transferring theory in association with remotely sensed frozen soil datasets was developed.In order to reduce the uncertainty of the simulation,the remotely sensed frozen soil information was used to monitor and modify relevant parameters in the process of model simulation.The remotely sensed information and numerically simulated spatial-temporal frozen soil processes were validated by in-situ field observations in cold regions near the town of Naqu on the East-Central Tibetan Plateau.The results suggest that the overall accuracy of the algorithm for discriminating freeze and thaw status of surface soil based on passive microwave remote sensing was more than 95%.These results provided an accurate initial freeze and thaw status of surface soil for coupling and calibrating the numerical model of this study.The numerically simulated frozen soil processes demonstrated good performance of the distributed numerical model based on the coupled water-heat transferring theory.The relatively larger uncertainties of the numerical model were found in alternating periods between freezing and thawing of surface soil.The average accuracy increased by about 5%after integrating remotely sensed information on the surface soil.The simulation accuracy was significantly improved,especially in transition periods between freezing and thawing of the surface soil.

Discussion on applying an analytical method to optimize the anti-freeze design parameters for underground water pipelines in seasonally frozen areas

Adopting the quasi-three-dimensional （Quasi-3D） numerical method to optimize the anti-freeze design parameters of an underground pipeline usually involves heavy numerical calculations. Here, the fitting formulae between the safe con-veyance distance （SCD） of a water pipeline and six influencing factors are established based on the lowest water temper-ature （LWT） along the pipeline axis direction. With reference to the current widely used anti-freeze design approaches for underground pipelines in seasonally frozen areas, this paper first analyzes the feasibility of applying the maximum frozen penetration （MFP） instead of the mean annual ground surface temperature （MAGST） and soil water content （SWC） to calculate the SCD. The results show that the SCD depends on the buried depth if the MFP is fixed and the variation of the MAGST and SWC combination does not significantly change the SCD. A comprehensive formula for the SCD is estab-lished based on the relationships between the SCD and several primary influencing factors and the interaction among them. This formula involves five easy-to-access parameters： the MFP, buried depth, pipeline diameter, flow velocity, and inlet water temperature. A comparison between the analytical method and the numerical results based on the Quasi-3D method indicates that the two methods are in good agreement overall. The analytic method can be used to optimize the anti-freeze design parameters of underground water pipelines in seasonally frozen areas under the condition of a 1.5 safety coefficient.

Experimental research on acoustic wave velocity of frozen soils during the uniaxial loading process

Ultrasonic P-wave tests of frozen silt and frozen sand were conducted during uniaxial loading by using an RSM^-SY5（T） nonmetal ultrasonic test meter to study the velocity characteristics of P-waves. The experimental results indicate that the P-wave velocity is affected by soil materials, temperature, and external loads, so the P-wave velocity is different in frozen silt and frozen sand, but all decrease with an increase of temperature and increase at first and then decrease with strain during the loading process. There is an exponential relationship between uniaxial compressive strength and P-wave ve- locity, and the correlation between them is very good. The characteristic parameters of acoustic waves can, to some extent, reflect the development of internal cracks in frozen soils during loading.

Stabilized effects of L-S cement-mixed batter pile composite foundation for existed warm frozen soil subgrade

In permafrost regions with warm frozen soil,subgrade thaw-collapse phenomenon commonly occurs,facing thaw collapse problems of the existed frozen soil subgrade,thus it is difficult to use traditional methods such as active cooling and passive protection technology to stabilize the existed warm frozen soil subgrade.This study derives a novel stabilizer method,a long-short(L-S)cement-mixed batter pile composite foundation to stabilize the existed warm frozen soil subgrade.To solve the thawcollapse problems in warm frozen soil subgrade,high water content and large compressibility characteristics were compared between soft soil and warm frozen soils.Theoretical analysis of heat conduction and numerical simulation of finite element model were used to study the freeze–thaw process and evaluate the stabilized effects of the L-S cement-mixed batter piles on the warm frozen soil foundation of the Qinghai-Tibet Highway.Furthermore,the thaw process and mechanical properties of foundation and piles were analyzed by introducing the hydration heat factor in the thermodynamic control equation.The results indicate that the thawing displacement of the existed warm frozen soil subgrade was reduced owing to the“support”and“grasp”effects of the L-S cement-mixed batter piles on the surrounding soil.The composite ground formed by strengthening the warm frozen ground with batter piles could considerably improve the bearing capacity of the existed warm frozen ground,effectively restrain the deformation of the upper embankment,and improve the strength of the ground.The analysis can provide method for the construction design of cement mixing batter pile foundation in cold regions.

Dynamic property tests of frozen red sandstone using a split hopkinson pressure bar

In this study, frozen red sandstone specimens were impacted by a Split Hopkinson bar (SHPB), with a velocity of 4.558 ~ 6.823 ms-1. The temperature of the specimens was maintained at -15℃ during the experiment. For comparison purposes, static uniaxial compression tests were conducted in advance using a freezing triaxial test machine. Four stress-strain curves were obtained in diff erent average strain rates. The test results suggested that when the average strain rate is low, the specimen strength changes gradually;but when it is high, its strength changes rapidly. When the average strain rate is 120.73 s-1, the peak value of stress is as high as 82.96 MPa, which is about two times that of the static compressive strength of 44.1 MPa. A constitutive model was established that was composed of the damaged, viscoelastic and spring bodies, and revealed the variations of compressive strength and strain for the frozen red sandstone under diff erent high strain rates. The test results also showed that the failure form was correlated to the average strain rate of the frozen red sandstone. When the average strain rate is low, the damage was only distributed on the specimen’s edges. However, as the average strain rate increases, the damage range extended to the central parts of the specimen. When the average strain rate reached 107.34s-1, the specimen was smashed.

Frozen shoulder:A systematic review of therapeutic options

Frozen shoulder is a common disease which causes significant morbidity. Despite over a hundred years of treating this condition the definition, diagnosis, pathology and most efficacious treatments are still largely unclear. This systematic review of current treatments for frozen shoulder reviews the evidence base behind physiotherapy, both oral and intra articular steroid, hydrodilatation, manipulation under anaesthesia and arthroscopic capsular release. Key areas in which future research could be directed are identified, in particular with regard to the increasing role of arthroscopic capsular release as a treatment.

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Field experiment of subgrade vibration induced by passing train in a seasonally frozen region of Daqing

The vibration characteristics and attenuation of the subgrade caused by passing trains in a seasonally frozen region of Daqing, China are investigated. Three field experiments were conducted during different times through the year, in normal, freezing and thawing periods, respectively, and the influence of the season, train speed and train type, is described in this paper. The results show that： （1） the vertical component is the greatest among the three components of the measured vibration near the rail track, and as the distance to the railway track increases, the dominant vibration depends on the season. （2） Compared with the vibration in the normal period, the vertical and longitudinal vibrations increase while the lateral vibration decreases in the freezing period. However, in the thawing period, the vertical and longitudinal vibrations decrease, and the lateral vibration increases. （3） As train speeds increase, the subgrade vibration increases. （4） The vibration induced by a freight train is greater than by a passenger train. These observations provide a better understanding of the vibration and dynamic stability of the subgrade and may be useful in developing criteria for railway and building construction in cold regions.

Studies on frozen ground of China

Permafrost in China includes high latitude permafrost in northeastern China, alpine permafrost in northwestern China and high plateau permafrost on the Tibetan Plateau. The high altitude permafrost is about 92% of the total permafrost area in China. The south boundary or lower limit of the seasonally frozen ground is defined in accordance with the 0 ℃ isothermal line of mean air temperature in January, which is roughly corresponding to the line extending from the Qinling Mountains to the Huaihe River in the east and to the southeast boundary of the Tibetan Plateau in the west. Seasonal frozen ground occurs in large parts of the territory in northern China, including Northeast, North, Northwest China and the Tibetan Plateau except for permafrost regions, and accounting for about 55% of the land area of China. The southern limit of short-term frozen ground generally swings south and north along the 25° northern latitude line, occurring in the wet and warm subtropic monsoon climatic zone. Its area is less than 20% of the land area of China.

Microstructure and strength features of warm and ice-rich frozen soil treated with high-performance cements

Warm and ice-rich frozen soil(WIRFS) exhibits lower shear strength due to the weak binding forces between soil particles and ice crystals. To enhance the strength of WIRFS, frozen soil was treated separately with Portland, Phosphate, Sulphoaluminate, Portland-Phosphate and PortlandSulphoaluminate cements. After the samples were cured under -1.0°C for 7 days, the microscopic pore distribution characteristics and the macro-mechanical properties of WIRFS were investigated using mercury intrusion porosimetry(MIP), scanning electron microscopy(SEM) and unconfined compressive strength(UCS) tests. To quantitatively analyze the laws of pore-size transformation and the variation of Hausdorff volumetric fractal dimensions for pre-and post-treated WIRFS, the CURVEEXTRACT and Image-Pro Plus(IPP) image analysis system has been developed for analysing SEM images of the soil samples. Statistics of the pore-area dimension and pore-volume dimension were calculated. The results reveal that the cement-based treatment of WIRFS can improve the cementation fill of soil pores and the bond forces between soil particles. There is an evident correlation between the microstructure characteristics and the mechanical properties of the treated WIRFS. As the fractal dimensions of pore-area decrease, the unconfined compressive strength of cement-treated WIRFS increases significantly. In contrast, as the fractal dimensions of pore-volume increases, the unconfined compressive strength decreases remarkably.